Oral toxicity of an essential oil from myrtle and adaptive liver stimulation.

The acute oral toxicity of an essential oil from the leaves of Myrtus communis (M) in rats was 3.7 ml/kg, and 2.2 ml/kg in mice. After repeated daily doses the toxicity decreased considerably and was calculated to be approx. 6.6 ml/kg after 10 days or 3 weeks pretreatment with M. Daily application of M during 10 days increased the relative liver weight of rats by 10, 18 and 28% at the dose levels of 0.5, 1.0 and 2.0 ml/kg. The hepatic endoplasmic reticulum (microsomal fraction) in the rats increased by 13.5, 24 and 33% after 10 days oral application of 0.5, 1.0 and 2.0 ml/kg of M, respectively. Hepatic cytochrome P-450 started to increase after 0.2 ml/kg, and reached 65% above controls after 10 days application of 2.0 ml/kg. Cytochrome b5 responded in a similar manner. The microsomal N-dealkylation of N-methylaniline increased 2.8-fold after daily administration of 2.0 ml/kg during 10 days. Continuous therapeutic application of M to humans in the magnitude of 1--2 ml daily is considered to be too low to influence the hepatic parameters.